Modified viruses have proven convenient vector systems for investigative and therapeutic gene transfer applications. Adenoviral vector systems present several advantages for such uses because they are generally associated with benign pathologies in humans, and the 36 kb of the adenoviral genome has been extensively studied. Adenoviral vectors can be produced in high titers (e.g., about 10.sup.13 particle/ml), and such vectors can transfer genetic material to non-replicating, as well as replicating, cells (in contrast with, for example, retroviral vectors which only transfer genetic material to replicating cells). The adenoviral genome can be manipulated to carry a large amount of exogenous DNA (up to about 8 kb), and the adenoviral capsid can potentiate the transfer of even longer sequences (Curiel et al., Hum. Gene Ther., 3, 147-154 (1992)). Additionally, adenoviruses generally do not integrate into the host cell chromosome, but rather are maintained as a linear episome, thus minimizing the likelihood that a recombinant adenovirus will interfere with normal cell function. Aside from being a superior vehicle for transferring genetic material to a wide variety of cell types, adenoviral vectors represent a safe choice for gene transfer, a particular concern for therapeutic applications.
A variety of recombinant adenoviral vectors have been described. Most of the vectors in use today derive from either the adenovirus serotype 2 (Ad2) or serotype 5 (Ad5), members of subgroup C. An exogenous gene of interest typically is inserted into the early region 1 (E1) of the adenovirus. Disruption of the E1 region decreases the amount of viral proteins produced by both the early regions (DNA binding protein) and late regions (penton, hexon, and fiber proteins), preventing viral propagation. These replication deficient adenoviral vectors require growth in either a complementary cell line or in the presence of an intact helper virus, which provides, in trans, the essential E1 functions (Berker et al., J. Virol., 61, 1213-1220 (1987); Davidson et al., J. Virol., 61, 1226-1239 (1987); Mansour et al., Mol. Cell Biol., 6, 2684-2694 (1986)). More recently, adenoviral vectors deficient in both E1 and the early region 4 (E4) have been used to substantially abolish expression of viral proteins. In order to insert the larger genes (up to 8 kb) into the adenoviral genome, adenoviral vectors additionally deficient in the nonessential early region 3 (E3) are used. Multiply deficient adenoviral vectors are described in published PCT patent application WO 95/34671.
The use of adenoviral vectors in investigative and therapeutic applications necessitates that the vectors be transported and stored for a period of time. During this period of storage, the adenoviral vectors desirably are maintained without significant loss of infectivity and/or viability. Adenoviral vectors can be stored frozen at very low temperatures, e.g., -80.degree. C., without significant loss of activity; however, the need for low temperature freezers, which are not widely available, limits the practicality of this approach. Lyophilization, or freeze-drying, is another option for storage of adenoviral vectors. This method has disadvantages as it is expensive, and, upon reconstitution, the adenoviral vector composition is often left for extended periods of time at room temperature (i.e., 20-25.degree. C.). Adenoviral vectors rapidly lose viability when stored at room temperature. Similar problems arise when adenoviral vectors are dried at room temperature.
In view of the above, there exists a need for further methods of, and compositions useful in, the storage or preservation of adenoviral vectors. In particular, there is a need for methods and compositions for storage of adenoviral vectors in a liquid state, rather than a dried or frozen state. The present invention provides such methods and compositions. These and other advantages of the present invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.